Hi Yakui, On Tue, Jun 24, 2008 at 10:39 PM, Zhao Yakui <yakui.zhao@xxxxxxxxx> wrote: > On Tue, 2008-06-24 at 21:17 -0700, Alok kataria wrote: >> On Tue, Jun 24, 2008 at 7:49 PM, Zhao Yakui <yakui.zhao@xxxxxxxxx> wrote: >> > On Tue, 2008-06-24 at 11:48 -0700, Alok Kataria wrote: >> >> Evaluates the _CRS object under PCI0 looking for producer resources. >> >> Then searches the e820 memory space for a gap within these producer resources. >> >> >> >> Allows us to find a gap for the unclaimed pci resources or MMIO resources >> >> for hotplug devices within the BIOS allowed pci regions. >> >> >> > It seems reasonable. >> > But if the resource obtained from the PCI0 _CRS method is incorrect, we >> > will get the incorrect pci_mem_start. >> >> Hi Yakui, >> >> What do you mean by the PCI0 _CRS being incorrect ? Why would the BIOS >> give a incorrect _CRS object ? >> Also we don't just take the value given from the _CRS method, we still >> read the e820_map to search for an unallocated resource. So even if >> (by chance) the _CRS method returns incorrect value we would still >> figure out if there is a collision with an already allocated resource. > In the patch the address obtained from the _CRS object will be passed > into the function of e820_search_gap. In such case maybe we will get the > pci_mem_start different with the e820_setup_gap. True..the whole idea behind doing this patch was to get a correct (different) value for pci_mem_start. We read the _CRS object over here to make sure that we assign the pci_mem_start from the address range which is reserved by the BIOS for PCI devices. Also this reading of _CRS object would be done before we start initializing the pci devices, i.e. before we start using the value of pci_mem_start, so the original value assigned by pci_setup_gap is just overwritten by this function. So that should be fine IMHO. Also we would still want the call for e820_setup_gap because there can be systems with no acpi support or acpi disabled > >> > >> > At the same time after the patch is applied, pci_mem_start will be >> > parsed in two different ways. >> >> Yes pci_mem_start would be initialized in 2 different ways but we >> still have to parse the e820_map the old way because there could be >> systems without ACPI. >> >> > If the result is different, maybe the >> > incorrect pci_mem_start will be used. >> >> Yeah, The result is different in my case. Though my BIOS reserves >> hotpluggable memory region, kernel doesn't respect that right now and >> just parses the e820_map to calculate the gap and pci_mem_start value. >> I have explained the problem in this mail. >> >> http://marc.info/?l=linux-acpi&m=121391675711763&w=2 >> >> Maybe nobody has seen this problem yet, because there are no systems >> out there with less than 4GB memory to start with and which allow >> memory hotplug. >> >> But still i don't understand what do you mean by, we can get incorrect >> pci_mem_start, in which case ? > > In the function of setup_arch the pci_mem_start will be parsed by > searching the e820 table. After the patch is applied, we will parse the > pci_mem_start again in the function of pci_acpi_scan_init and it will > override the value parsed in the function of setup_arch. If the > pci_mem_start is incorrect in the second case, maybe it will have side > effect. Yes it will override. But how can the value be incorrect in the second case. As explained in my previous mail we still parse the e820_map to check if we have unclaimed resources between start_address (that read from _CRS) to 2^32. So even if this start_address is wrong we would catch that during parsing e820_map. But again why would the _CRS return incorrect values, are you talking about errors in BIOS ? Thanks, Alok -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
